High functionality devices utilizing the spin of the electron are called spintronic devices and expected to provide a new technology that will surmount limits of conventional semiconductor devices. Technologies pertaining to spintronic devices are disclosed in, for example, patent documents 1 to 9.
Nowadays, spin current that does not involve electric current (pure spin current) has been attracting attention, as new functionalities of spintronic devices and techniques for generating, transporting, detecting it have been gradually developed.
For example, according to an existing method, electric current flowing in the interface between a non-magnetic material and a ferromagnetic material generates a pure spin current. Specifically, a thin non-magnetic wire is kept in contact with a ferromagnetic body. As an electric current flows in the interface of the non-magnetic material and the ferromagnetic material, a spin polarized current (pure spin current+electric current) flows from the ferromagnetic material into the non-magnetic material. If only one side of the thin non-magnetic wire forms a closed circuit with the current source, an electric current flows in the circuit side thin non-magnetic wire, while no current flows in the other side thereof. However, a spin current injected from the ferromagnetic material diffuses toward both sides of the thin wire even in a portion where there is no electric, current flows. This is called a pure spin current. One method of generating/detecting a pure spin current is a method utilizing the spin Hall effect of non-magnetic materials. Technologies pertaining to the spin Hall effect are disclosed in, for example, non-patent documents 1 to 6.
Heretofore, 5d transition metals such as Pt have been usually used to generate/detect a pure spin current utilizing the spin Hall effect. However, the conversion efficiency (i.e. the efficiency of conversion between electric current and spin current) with them is very low. It has been reported that a very high conversion efficiency was achieved with the use of Au, but the inventors of the present invention and other researchers have not been able to achieve such a high conversion efficiency with Au (non-patent document 7). Thus, data about Au lacks reproducibility (reliability), and it is considered that the conversion efficiency is highest with Pt.
In existing spintronic devices, ferromagnetic bodies are used as spin injection sources and spin detection sources. However, with a decrease in the device size, the distance between ferromagnetic bodies used as spin injection and spin detection sources also have been decreased, and it is also necessary that the size of the ferromagnetic bodies themselves be made small. This will cause magnetostatic coupling between the ferromagnetic bodies, which can adversely affect the operation characteristics (in particular, magnetic field response) of the device. The utilization of the spin Hall effect or the inverse spin Hall effect of a non-magnetic material in spin injection and spin detection will eliminate this problem. However, there is a problem of low conversion efficiency with the conventionally used materials.